(a) Field of the Invention
The present invention relates to a method of preparing a super absorbent polymer. Particularly, the present invention relates to a method of preparing a super absorbent polymer having high centrifuge retention capacity and high permeability.
This application claims priority to Korea Patent Application No. 10-2013-0004455 filed on Jan. 15, 2013, and the contents are herein incorporated by reference.
(b) Description of the Related Art
Super absorbent polymer (SAP) is a synthetic polymer material having a function of absorbing water about five hundred times to about one thousand times the weight of itself, and it has been differently named as super absorbency material (SAM), absorbent gel material (AGM), and so on by developing companies. The SAP disclosed above started to be commercialized for sanitary items and is now widely used to water combination soil for horticulture, water-stop materials for civil engineering and construction, nursery sheets, freshness preservatives in the food distribution field, poultice materials, and the like, in addition to the sanitary fittings like paper diapers for babies.
An inverse suspension polymerization method or an aqueous polymerization method is known as a method of preparing super absorbent polymer. For example, the inverse suspension polymerization is disclosed in Japanese Patent Publication Nos. Sho56-161408, Sho57-158209, Sho57-198714, and so on. As the aqueous polymerization method, a thermal polymerization method polymerizing a hydrogel polymer while fracturing and cooling the same in a kneader equipped with a plurality of spindles, and a photo-polymerization method that exposes a high-concentrated aqueous solution on a belt to a UV ray and the like so as to carry out the polymerization and the dry at the same time are known.
Generally, the hydrogel polymer obtained by said polymerization reaction comes into the market in the form of powder after it is dried and milled.
On the other hand, there is a method of performing a polymerization and then a surface crosslinking reaction in order to obtain a super absorbent polymer with more excellent properties. Generally, the surface crosslinking reaction is accomplished by spraying a surface crosslinking solution obtained by adding a crosslinking agent to water on the surface of the polymer and, after agitation, applying a heat to cause the crosslinking reaction. With a view to controlling the penetration speed and depth of the surface crosslinking solution into the polymer particles, alcohols, polymers, or the like can be added to regulate the surface thickness of the polymer cross-linked.
The above-described method, however, leads to non-uniform application of the surface crosslinking solution on the surface of the super absorbent polymer and offers high permeability but a decrease in centrifuge retention capacity and absorption under pressure, ending up with the difficulty in acquiring satisfactory properties in all aspects.